Art of cracking hydrocarbons



c. E. FORWARD 2,007,081

ART OF CRACKING HYDROCARBONS Filed Nov. 25, 1927 2 Sheets-Sheet l July 2, 1935.

WEEK VFL VE c. B. FORWARD ART OF CRACKING HYDROCARBONS Filed NO V. 23, 1927 2 Sheets-Sheet 2 C-B- FRWFIRD Patented July 2, 1935 UNITED STATES PATENToFI-lc I ART 0F CRACKI'NG HYDROCARBONS Chauncey B. Forward, Urbana, Ohio, assigner, by mesne assignments, to Forward Process Comparis@` Dover,

Delaware Del.,

a corporation of Application Nvember 2s, 1927, serian No; 235,206

7 Claims.

hydrocarbon product. This application is in part.

a continuation of my co-pending applications Serial Nos. 318,484, 665,537 and 682,477 filed August 19, -1919, September 24, 1923, and December 24, 1923, respectively.

It has been known -that cracked distillates obtained by cracking special fractions derived from certain naphthene and asphalt base crude oils have to a limited extent the ability to inhibit detonation at slightly higher pressures than those encountered in internal combustion engines of the present day automobile. It is also known that in exceptionally high temperature cracking operations such as those carried out in connection with the manufacture of gas for illuminating purposes, a low percentage of the stock charged may be obtained as a by-product distillate or,

condensate having good detonation inhibiting characteristics, but such distillates or eendensates have the disadvantage of ordinarily containing a relatively high percentage of unsaturated compounds which decompose readily with the formation of gum which it is practically impossible to remove Without excessive loss of the more stable unsaturated compounds. Such distillates also have a very offensive odor. Further, the major portion of the'charging stock is converted into a permanent gas and only a relatively small yield of a condensate boiling within the range of present day internal combustioncoke. This assumption has apparently been corroborated by the fact that all of the very high temperature vapor phase cracking processes heretofore developed, so far as I am aware, have been accompanied by excessive coke formation and the diiculties incident to this vformation of coke and carbon-like materials have constituted a serious engineering problem and frequently resulted in disaster. I have discovered that this.

coke formation is unnecessary in the vapor phase cracking of petroleum oilsr even when very high temperatures are employed, and further that by vapor phase cracking at high temperature so conducted as to avoid coke formation, a distillate product is'produced 'which is chemically quite different from the distillate products of ordinary cracking processes and which has desirable physical characteristics superior to any product now known. The formation of these products is apparently due to the accurate control of intermediate reactions hitherto. unsuspected which' produce a product that is destroyed, if it is ever formed at all, under the conditions existing in ordinary cracking processes. v,

Distillate products produced. by thev improved process of the invention are characterized by their highcritical compressionwhen used as motor fuels in internal combustion engines; their ability to increase the critical compression of other petroleum distillates with which they .may be blended; their high specific gravity relative to the specific gravity of ordinary petroleum distillates having a corresponding range of boiling points, their stability and relative freedom from gum-forming constituents in their crude state and Without further treatment and their superior ability to develop power when used asA motor fuels in internal combustion engines, especially in engines having a high compression ratio.

The process of the invention is adapted to produce a distillate product having a high critical compression from even the most refractory petroleum oils and distillates, including pure parafne base oils from which the distillates obtained by ordinary Ycracking processes are notable for their detonation characteristics even at low pressures, with conversion of only a comparatively small percentage of the charging stock into fixed gas and with' substantially no coke formation. For example, I have produced from a purely parafline base gas oil by the improved processof the invention, a largeyield of a distillate product L'that would operate successfully as a motor fuel in an internal combustion engine having a compression ratio greater than 11 to l, Without audible detonation under conditions, other than compression ratio, at which it was impossible to -operate Without audible detonation with a compression ratio greater than 4.3 to 1, when using a straight run Pennsylvania gasoline/as the motor fuel and at which it was impossible to operate without audible detonation with a compression ratio greater than 5.43 to 1 when using a blend of 50% pure benzol and 50% straight run Pennsylvania gasoline as the motor fuel. Further, when using samples of the improved distillate product as the motor fuel, the engine operated satisfactorily, though with regular detonation, when the compression ratio was increased to greater than 14 to 1.

According to the process of the invention, an advancing stream of the oil, preferably a gas oil or heavy naphtha distillate, is heated, vaporized and the generated vapors superheated to a temperature substantially in excess of 'their boiling point at the pressure employed so that the major part oi the cracking reaction takes place in the vapor phase. The superheated oil vapors are then subjected to a digesting operation for a considerable period of time at a uniform and accurately controlled temperature during which heat is supplied to the vapors at substantially the rate at which heat is absorbed in the reactions taking place. The stream of oil or vapors during the heating operation and during the digesting treatment above referred to is maintained in motion at a relatively high velocity and is heated by heat transfer from a heating medium positively circulated preferably countercurrent to the ow of'oil and vapors and in indirect contact heat exchanging relation therewith. I find it advantageous to employ a gaseous heating medium so that all difficulties incident to solidification and the necessity of supplying latent heat of vaporization are avoided over the temperature range employed and a more even distribution of the heating eifect obtained. When employing a gaseous heating medium, a relatively high velocity of flow over the heating surfaces should be maintained. The temperature of the heating medium is maintained only slightly higher than that of the oil or vapors being heated or undergoing the cracking reaction so that a gradual and uniform heating eiiect is obtained. The cracked vapors may advantageously be subjected to a further digesting treatment in an enlarged heat insulated zone during which no heat is supplied from an external source and the vapors are maintained above their cracking temperature by their self-contained heat. An additional amount of conversion takes place during the last named digesting operation.

The cracked vapors from the digesting operation are preferably chilled suddenly from at or above the cracking temperature to below the cracking temperature, for example, by injecting a cooling medium, such as water or a relatively cool liquid hydrocarbon into the vapor stream at the point of discharge from the digesting zone. The injection of a cooling liquid into the vapors discharged from the digesting operation before their temperature 'has been materially reduced serves to prevent the formation of carbon incrustations in any subsequent part of the system in such a manner as to foul the apparatus. Water may advantageously be employed as the cooling medium because of its high latent heat.

The entire charge of cracked vapors may be condensed to form a single overhead distillate and any desired fraction separated therefrom by subsequent redistillation, or the vapor stream may be chilled from at or above the cracking temperature to below the cracking temperature, but not to below the condensing point of the major portion of the cracked vapors, and the vapors remaining uncondensed subsequently fractionally condensed in a suitable dephlegmator to secure any desired end boiling point distillate without redistillation. The fresh oil supplied to the stream may be preheated by heat exchange with the hot vapors and the cooling action of the fresh oil utilized to eiect partial condensation of the vapors. The pressure maintained on the vapors during the cracking treatment will vary with the character of the product desired and the character of the oil 'used as charging stock. For example, the digesting operation may be carried out under substantially atmospheric pressure and the oil supplied to the heating coils at the pressure necessary to maintain the desired rate of ilow therethrough. Or, a pressure in excess of 250 pounds per square inch may be maintained on the vapors in the enlarged digesting zone and the oil supplied to the heating coil at a pressure of from about 400 to 600 pounds per square inch or higher. In general, the higher the pressure employed the greater will be the yield and the higher the quality of hydrocarbon constituents obtained which are of value as detonation inhibitors.

The process of the invention will be further described in connection with the accompanying drawings which illustrate in a diagrammatic and conventional manner f one form of apparatus adapted to carry out the process of the invention, but it is intended and will be understood that this further description and illustration are for the purpose of exemplication and that the invention is not limited thereto.

Fig. 1 is a conventional representation in elevation and partly in section of one form of apparatus adapted to carry out the process of the invention.

Fig. 2 is a diagrammatic representation in elevation of a modification of the type of apparatus illustrated in Fig. 1.

Referring to Fig. 1 of the drawings, A is a boiler and superheater similar to that described and illustrated in my former application Serial No.4

ameter andk 18 feet long, the coils were built of 3A- inch pipe and were'each approximately 500 to 600 feet in length. 'I'he drum I0 is provided with the cracking or digesting coil 20. This coil may advantageously be considerably longerpthan any one of the coils I I to I9 and is connected to form a continuation of the latter and to discharge into the digesting chamber 2l. For example, in the installation above referred to the drum I0 was about 18 feet long and 24 inches in diameter and the coil 20, constructed of l inch pipe, approximately 2300 feet in length. The latter portion of the continuous coil formed by the units II to 20 may advantageously be of a slightly greater diameter than the initial portion toA decrease the resistance to flow due to expansion of the generated vapors. in series by connections 38 arranged to convey the highly heated gaseous heating medium successively therethrough and are heavily heat insulated to prevent loss of heat by radiation. Connection 31 is arranged to convey superheated steam from the superheater A to the drum I0. Branch connections 4I and Ma are provided to The drums I0 to I are connected ranged therein. A draw off connection 33 leads t of water supplied by the pump 42a. is substanpermit superheated steam to be supplied direct- 1y to the chamber 2| and auxiliary. chamber 22, when desired, for example; during preliminary heating of the apparatus.

In the installation above referred to, the chamber 2| consists of a vertical drum approximately 3 feet in diameter and 23 feet in length. This chamber is preferably heavily heat insulated,-

though if desired loss of heat therefrom by radiation may be prevented by circulating heating gases of the same or slightly higher temperature than the oil vapors thereover.

Chamber 2| is shown in communication with heat exchanger 21 through valved connection 29.

AA jet 30 in the connection 29 adjacent chamber 2| is arranged to permit a cooling iluid, such as water, to be injected in regulated amounts into the stream of vapors asA they are discharged from the chamber 2|. The heat exchanger illustrated comprises a shell 3|, having a coil 32 arfrom the lower part of the heat exchanger. A vapor connection 34 leads from the top of the heat exchanger to the water cooled condenser 35i The fresh oil pump 36 is connected to the upper end of the coil 32 and the lower end of the coil is connected to one end of the heating coil l! in the drum or jacket i. The heating medium, for example superheated steam, is 4conveyed from the heater A While at its maximum temperature through connection 3l to drum l0, where it crculates rapidly over the coil of pipe therein, and then passes consecutively through drums 9 to l from whence it is conveyed at a reduced temperature through connection 42 to steam receiver 39. The pressure in the steam receiver 39 is maintained a sumcient amount lower than the pressure in the heater A to insure a rapid ow of the heating medium over the heating coils.

Steam withdrawn from the receiver 39 at a reduced temperature may be reheated and again employed as a heating medium in another similar apparatus, or returned to the original heater and recycled through the same system, or it may be employed as industrial steam for any other purpose desired. Compressor 40 is arranged to withdraw steam from the receiver 39 and increase the pressure on the steam so withdrawn an amount suicient to overcome the frictional resistance to ow through the system, when it is desired to recycle the steam-through the' original system.

Reheating the steam has the advantage of requiring only superheat to raise the temperature of the steam to any desired point, thereby avoiding the necessity of supplying latent heat. f

I viind it advantageous to maintain a relatively high pressure on a gaseous heating medium so as to increase the effectiveness of the heat transmitting surfaces, through which heat is transmitted to the oil or vapors. In this connection I have found steam to be a particularly advantageous heating medium because of its high specic heat and the convenience of securing large amounts under a high pressure and at a high temperature. Where steam is to be the heating medium and an arrangement of generator and superheater, in which .an advancing stream of water is vaporized and superheated while passing through a single continuous coil is employed, as illustrated in Fig. 1, the compressor 40 may kadvantageous be arranged to introduce the compressed steam into the boiler A at approximately the point at which vaporization of the stream tially complete.

Where it is desired to employ a superheater independent of the boiler, as in the arrangement illustrated in Fig. 2, the ycompressor 43 may bearranged to discharge steam withdrawn from receiver 39 through line 50 containing check valve 5| directly into the line communicating between the boiler 44 and superheater 45. In order to secure accurate control, the arrangement of apparatus illustrated in Fig.A 2 may with advantage be operated so that the entire quantity of steam passing through the superheater 45 and drums |0 to is supplied directly from the receiver 39 by the compressor 43, and such additional steam as is necessary to compensate for anyV slight losses throughout the system supplied directly to the drum 39 from the boiler 44 through connection 46. When operating in this manner the valve 48 is closed and the valve 49 opened.

An arrangement of apparatus similar to that just described is also advantageous where a gaseous heating medium other than steam, for example, nitrogen, carbon dioxide, or other gaseous substances, preferably inert to reduce lire hazard, is employed. When so operating, circulation of the heating medium may be maintained entirely by the compressor 43, and such additional gaseous substances as are required to compensate for leakage from the system introduced directly to the receiver 39 from any suitable source of supply, for example through connection 47|. s

In the operation of the apparatus illustrated in Fig. 1, fresh oil supplied by the pump 39 is forced through coil 32 in heat exchanger 3i, where it is initially heated by the hot cracked vapors, to the inlet of coil il and passed serially through coils li to2@ in countercurrent ow below the temperature of the steam in the drum y I0. While the hig'hly heated oil vapors are traveling through the coil 20 in a stream of restrictedcross section they are maintained at a high temperature :fora prolonged period of time. Since no vapors are withdrawn at an intermediate point in the coil 29 'and the flow of vapors therethrough is maintained at a high velocity, substantially no segregation of the heavier and rlighter constituents is permitted. The hot cracked vapors discharged into the vheat insulated digesting chamber 2| through connection 23 may continue to undergo a cracking reaction and as their velocity is materially reduced in the digesting chamber any small amount of free carbon that may be released from the vapors may be permitted to settle to the bottom of the digesting chamber in the form of a light inely divided dry powder resembling carbon black. This carbon ,which is negligblewin amount and ordinarily will not exceed .10% of the total oil charged may be blown oi from time to time to.

the auxiliary chamber 22, without. interrupting the cracking operation, when it is desirable to'- collect it separately. If it is not desirable to separately collect this negligibly small amount of free carbon, the finely divided powder may be carried on through the system with the vapor stream, for example, by arranging the discharge end of connection 23 suiiiciently close to the lower-end of chamber 2i so that the blast of va- 'pors will prevent settling.

The temperature of the cracked vapors in the chamber 2| to be most advantageously employed will vary from about 875 to 1050 degrees F. depending on the kind of oil being treated and the character of the distillate itis desired to obtain. The vapors escaping from chamber 2| are suddenly chilled to below their cracking temperature by injecting water or other suitable cooling fluid into the vapor stream at the point of discharge from the digesting chamber and .before the temperature of the vapors has been materially reduced below the temperature at which they were maintained in the digesting chamber. The injection of a sufficient quantity of water to reduce the temperature lof the oil vapors to about 700 degrees F. has been found in practice to satisfactorily prevent the formation of carbon incrustations in any part of the apparatus through which the vapors or condensate thereof are subsequently required to pass. The vapors leaving the chamber 2i, and subsequent to the chilling operation above referred to, may be advantageously passed through the heat exchanger 21 in heat exchanging relation with the fresh oil supplied to the system through the coil 32 to recover a-portion of the heat contained therein.

When the apparatus illustrated is so operated the vapors will be subjected to a reiiuxing action by the cooling eifect of the fresh oil and the condensate so formed may' be drawn oft' through connection 33. Vapors escaping uncondensed from the heat exchanger may be passed directly to the water cooled condenser 435 and condensed therein to form a single overhead distillate, which may be'fractionally redistilled as desired, or the vapors escaping from the heat exchanger may be fractionally condensed in a suitable fractional condenser to secure. products of the desired boiling pointrange "i,

The uncondensed vapors and gases ,escaping from the final condenser may be treated by absorption or compression for the recovery of readily condensible constituents contained therein. 'I'hese gases furthermore are particularly rich in constituents suitable for the production of -alcohols and other organic derivatives or substitution products.

Due apparently to the gradual heating of' the oil and vapors in the coils Il to I8 and the prolonged exposure of the oil vapors to high temperature in the coil 20, the discharge temperature of the oil vapors from the latter is verycritical and substantial variationsin the temperature at this point, as well as in the pressure and the' rate of throughput, will cause a marked variation in the character, not only of the composite distillate product obtained,but also in the character of fractions having similar boiling point ranges. The character of the distillate is also materially affected by the length of the time of exposure to high temperature as governed by the length of the coil 20. The exact temperatures, pressures and rate of throughput to be most advantageously employed in a given apparatus will, of course, vary with the character of the distillate product it is desired to obtain, as well as with the character of the initial chargingstock. The

effects of variation in the temperatures employed and in the time of exposure of the oil to high temperatures as governed by variations in the length of the coil 20 may be best illustrated by specific examples of runs made under different operating conditions. I do not know the exact chemical composition of certain components of the distillateproducts that may be produced by the improved process of the invention, but some of their'physical characteristics differ radically from all other natural or cracked petroleum distillates of a similar range of boiling points of which I am aware. For example, I am not certain that all of the constituents referred to as aromatic hydrocarbons are true members of the aromatic series and in referring to aromatic hydrocarbons, naphthenes and unsaturated hydrocarbons in the description of the distillates or fractions thereof when operating under different conditions, as hereinafter described, and in defining the distillate products in the claims appended hereto, I refer to such constituents as react similar to aromatic hydrocarbons, naphthenes and unsaturated hydroca'rbons when a distillate containing them is subjected to *the following tests developed by Dr. J. R. Withrow, Professor of Chemical Enginearing, Ohio State University, Columbus, Ohio, and hereinafter described.

Unsaturated hydrocarbons A 100 cc. charge of the product to be tested is distilled in a 100 cc. Engler (A.' S. T. M.) distilling flask, using the standard Government and A. S. T. M. equipment as used in the distillation test for gasoline. This distillation is stopped immediately upon the appearance of cloud in the distilling iiask and the temperature at which cloud appears noted. The residue in the flask is discarded. The distillate obtained in the above operation is treated with sulphuric acid, in the volume ratio of acid to oil of 2:1. The mixture is agitated for fifteen minutes and then allowed to settle at least twelve hours. The volume of the oil layer formed on settling is measured and the percent decrease of this lvolume is calculated on the basis of the distilled fraction. 'Ihis calculation gives the percentage of .unsaturated hydrocarbons that have dissolved in the acid layer as reaction products. A The acid treated oil is washed with watenneutralized with la 10% solution of sodium hydroxide.

allowed to settle in a separatory funnel, the aqueous layer drawn off arid the oily layer then redistilled in the .distillation apparatus above described, and to the temperature above noted. The volume of the residue of the second distillation is measured and is calculated as a percentage .of the first `distillation fraction. This represents the percentage of the unsaturated hydrocarbons that have been polymerized during the acid treatment. 'I'his value, added to the percentage of unsaturated hydrocarbons dissolved by the sulphuric acid, gives the total percentage of unsaturated hydrocarbons in the original dis- .tillation fraction. c

Aromatic hydrocarbons Into a cc. burette provided with a glass water bath are put 20 cc. of the second distillation fraction (freed from unsaturated bodies) and 50 cc. of nitrating mixture added slowly with mixing (by tilting tube) and cooling (passing cold water through water jacket). The nitrating mixture consists of nitric acid 25%, sulphuric acid 58% and water`1?7%. This operation should require from 15 to 60 minutes and great care must be'taken to avoid heating, which may cause side reactions and possible explosion, and errors inl this the percentage in the first distillation fraction can be readily calculated.

Naphthenes The oil from the nitration treatment is washed with water and a 10% solution of sodium hydroxide and subsequently thoroughly dried'with calcium chloride. The aniline value is determined on this dried oil, which is a mixture of paraiine and naphthene hydrocarbons. Ten cc. of

`freshly distilled anilineand an equal volume of the oil are placed in a test tube that is jacketed by a larger test tube. Into the smaller test tube ^are placed a thermometer (calibrated in 0.1 degrees C.) and a stirring rod. The mixture is heated until the cloud disappears and the temperature at this point is read. The heating is continued until the solution is just above the cloud point and then allowed to cool until the cloudiness reappears. This cloud point is read to 0.1 degrees C. Under the conditions of the test, the paraiine hydrocarbons are completely miscible with aniline at '70 degrees C., and the cloud point is depressed 0.3 degrees C. 'for each 1% of naphthene hydrocarbons present. The diierence between the temperature at the cloud point and '70 degrees C. divided by 0.3 will give the percentage of naphthene hydrocarbons in the oil from the nitration treatment. This percentage may then be calculated back to the original distillation fraction to find the percentage of naphthene in the original fraction. r f

- Paranes Thepercentage of parafline hydrocarbons in the original distillation fraction is obtained by subtracting the sum of the percentage of unsaturated, aromatic and naphthene hydrocarbons from 100.

In order to determine the detonation inhibiting characteristics of the distillates obtained by varioil, and blends of this gasoline with pure benzolv boiling substantially entirely within a range of 1 degree C. The straight run Pennsylvania distillate employed in making these tests was a distillate having an initial boiling point of 137 degrees F. and an end boiling point representing 96 over at 406 degrees F. 1

The engine used in making these tests '-was a 3 X 4 Isingle cylinder, water cooled, four cycle engine of the valve in head type. All tests were made witha fixed spark advance of 20 degrees and an engine speed of 1080 revolutions per minute. The torque of the engine was measured by a cradled generator. 'I'he engine was so constructed that the compression ratio could be va- .ried over a considerable range while/the engine was operating, without material change in the valve timing or lift. The compression ratio at which detonation was rst audible was determined by ear and carefully checked by different operators. IFurther tests were -made at higher compression ratios Vto determine the power characteristics of the`various fuels beyond the point of audible detonation. Indicator diagrams were obtained by means of a high speed indicator arranged to record a diagram representing the composite of 'several hundred explosions.

In making each test theengine was permitted to run long enough after all adjustments'had been completed to permit conditions to become constant. The carburetor was adjusted to give maximum power output with each fuel tested when operating at a fixed compression ratio, and the adjustments so secured used with all tests which were made of thatfuel. All the variable compression tests were made-With the carburetor throttle held wide open, the load on the generator being varied until the engine speed was 1080 R. P. M. The temperature of the `cooling water during all tests was maintained at 212 degrees F.

The following examples are given to illustrate the flexibility of the operation of the'cracking ap.- paratus illustrated and described. The most advantageous method of operation will, of course, depend on the market demand, as the apparatus may be operated to-produce distillates representing different quantities of the oil charged and having widely diierent physical characteristics. Of the following examples the runs designated as Examples 1 and 2 were carried out in anapparatus substantially similar to the installation above described, in which a coil approximately 350 feet in length was employed as the digesting coil 20,- whereas in the other runs a much longer coil was substituted therefor. The coil used in the latter tests was approximately 2300 feet in length, and a comparison of two runs made with the different equipment, but with substantially the same temperatures, pressures and rate of throughput will clearly illustrate the'eiect of the length of time of exposure to high temperatures on the quantity and character of the distillates obtained.

In each of the following runs steam .was supplied from the boiler and superheater- A at a temperature of about 1150 to 12,00 degrees F. and freshgoil supplied to the system at a rate f labout gallons per hour.

The fresh oil charged was `a 38 degree B. gas

oil fraction` from a Pennsylvania type crude oil.

The boiler was operated so as to supply steam at a pressure of about 250 pounds per square inch and the steam receiver 39 maintained at a pres-A sure of 225 pounds per square inch'more or less as required to maintain the necessary ow of steam through the drums 10 to 1. The vapors in the digesting chamber 2 twere maintained under a pressure of about 225 pounds, under which conditions a pressure of labout 400 to 450 pounds per square inch was required at the pump 36 to maintain a flow oi 180 gallons per hourof fresh oil through the heating coils. An appreciable drop in temperature of the steam between the heater A and the drum I0 was noted, andafter substantially constant operating conditions were obtained the average temperature of the steam inthe drum I0 was held at about 15.to 30 degrees F. higher than heating coil 20.

Example No. 1

Steam was circulated through drums I0 etc. at a rate regulated to maintain the temperature of the oil vapors discharged from the coil 20 at approximately 975 degrees F. 'I'he vapors discharged from the digesting chamber 2| were condensed to form a single crude distillate product, which represented approximately 80% of the total oil charged, and had a gravity of degrees B. Approximately 70% of the crude distillate was obtained as an overheaddistillate by subsequent redistillation. The redistilled product had an end boiling point slightly below 437 degrees F., a gravity of 56 degrees B. and contained slightly in excess of 20% aromatic hydrocarbons. When tested as a motor fuel the redistilled product exhibited anti-detonating characteristics greatly superior to a blend comprising benzol and 50% straight run Pennsylvania gasoline. About 4% of the fresh oil charged to the system was recoverable from the uncondensed vapors as a light distillate.

Example No. 2

Steam was circulated through drums I0 etc. at a rate suiiicient to maintain the temperature of the oil vapors discharged from coil 20 at approximately 1020 degreesv F. The vapors discharged from the digesting chamber 2| were condensed to form a single crude distillate product, which represented approximately 75% of the total oil charged. 'Ihe 'crude distillate had a gravity of about 37 degrees B. On subsequent redistillation approximately of the crude distillate was obtained as a 52 degree B. overhead distillate Example No. 3

I This run was made using a digesting coil approximately six times as long as the digesting coil employed in the runs described in Examples 1 and 2. Steam was circulated through drums i0 etc. at a rate suicient to maintain the temperature of the oil vapors discharged from the coil 20 at approximately 1050 degrees F. The vapors discharged from the digesting chamber 2| were condensed to form a single crude distillate product having a gravity of about 16.5 degrees B., .which represented approximately of the total oil charged. On subsequent redistillation 50% of the crude distillate was obtained as an overhead distillate having a gravity of 32.8 de- Agrecs B. and an end boiling'point of approximately 437 degrees F. About 12% on the fresh oil charged through the system, was recoverable from the uncondensed gases as a light distillate. The redistilled product on analysis was found to contain 82.9% aromatic hydrocarbons, 17.1% other unsaturated hydrocarbons andno naphthene or paraine hydrocarbons. A blend composed of 40% of the above distillatev and 60% u' straight run Pennsylvania gasoline was found to have anti-detonating characteristics greatly superior to all blends of pure benzol and straight run Pennsylvania gasoline regardless of the ben- -zol content of the blend when tested as a motor fuel in an internal combustion engine. The 32.8 degree B. distillate when tested alone as a motor fuel was found to operate satisfactorily at all compression ratios below 11.2 to l without audible detonation under conditions, other than compression ratio, at which a straight run Pennsylvania gasoline would not operate Without audible detonation when the compression ratio was increased to more than 4.3 to 1. Further, a blend of 50% of the 32.8 degree distillate with 50% straight run Pennsylvania gasoline was found to operate without audible detonation at a compression ratio of 6.45 to 1 under conditions other than compression ratio at Which the straight run Pennsylvania would not operate Without audible detonation when the compression ratio was increased to in excess of 4.3 to 1 and at which a blend composed of 50% pure benzol and 50% straight run Pennsylvania gasoline would not operate without audible detonation when the compression ratio was increased to 5.43 to 1. It will be apparent that the increment of increase in permissible compression ratio due to theaddition to the straight run Pennsylvania gasoline of an equal volume of the 32.8 degree B., distillate product is approximately 100% in excess of the increment of increase due to theaddition of an equal volume of pure benzol.

From the results obtained in a series of tests using blends of various percentages of the 32.8 degree distillate with straight run Pennsylvania gasoline,l andanother series of similar tests using blends of the same' percentages of pure benzol with straight run pennsylvania gasoline, it was observed that as the percentage of pure benzol Was increased the compression ratio at which detonation Was first audible initially increased, but at a decreasing rate, reached a maximum when a 'blend containing approximately 50% benzol was used, and had decreased materially before the benzol content of the blends reached while, as the percentage of the 32.8 degree B. distillate was increased the compression ratio at which detonation was first audible increased at a consistently increasing rate which became very marked when the percentage of the distillate in the blend exceeded 30%.

A similar series of tests Was made on a commercial gasoline which had anti-detonating characteristics slightly superior to those of the straight run Pennsylvania gasoline and on blends of the above distillate and of pure benzol with the commercial gasoline, using the same product for blending in both cases. In these tests it was noted that the ratio of the increment by which the compression ratio could be increased Without audible detonation by the addition of a given percentage of the above distillate to the commercial gasoline relative to the increment by which the compression ratio could be increased Without audible detonation by the addition of a similar percentage of pure benzol to the commercial gasoline was appreciably greater than the corresponding ratio of the increments by which the compression ratio could be increased Without audible detonation by the addition of the same percentage of this distillate and of pure benzol respectively to samples of the straight run Pennsylvania gasoline. This was particularly noticeable with respect to the blends of lower-benzol content.

It was also observed in making the above tests that when running the engine under full load over motor fuel.

Awioo c. c. sample or this 32.8 degree B. distillate when evaporated in a copper dish was found to leave about 60 mgs. of gum.

Example No. 4'

A run was made using the same digesting coil 20 as employed in the run described in Example No. 3, but maintaining the temperature of the voil vapors dischargedfrom the coil 20- at about 980 degrees F. The vapors discharged from the digestingchamber 2| were condensed as a single crude distillate product, having a gravity of 25 degrees B., representing about '70% of the total oil charged. About 8% of the oil charged was recoverable from the uncondensed gases as a light distillate. The effect of the time of exposure to the high temperature maintained in the digesting coil due to the greater length of the coil will be evident from a comparison of the gravity of the product and the yield obtained in this example as compared with those obtained in the run given as Example No. l, during which substantially the same temperatures were maintained although a much shorter digesting coil 20 was employed.

Example No.

Another run was made using the same apparatus as employed in the runs given as Examples Nos. 3 and 4. During this run steam was circulated through the drums l0 etc. at a rate suflcient to maintain the temperature of the oil vapors discharged from the coil 20 at a temperature of 1030 to 1040 degrees F. The vapors discharged from the digesting chamber 2l were condensed as a. single crude distillate product, having a gravity of- 22 `degrees B., representing about 68.5% of the total oil charged. An analysis of the crude distillate showed it to contain 96% unsaturated and aromatic hydrocarbon compounds. On subsequent redistillation approximately 53% of the crude distillate product was obtained as an overhead distillate having a gravity of 37.5 degrees B. and an end boiling point slightly below 43.7 degrees F. In addition, about 10% on I the total oil charged was recoverable from the uncondensed gases as aT light distillate.

A further portion of the crude distillate obtained from the run given as Example No. 5 was fractionally distilled, the cuts being made to give fractions having gravities as follows:

Analysis of the 39.7 degree B. fraction which include all of the lighter constituentsfcontained in the crudedistillate product showed-it to contain 25.6% unsaturated hydrocarbons, 63.4% aromatic hydrocarbons and 11.0% naphthene and paraffine hydrocarbons. 'Analysis of the 22.6 degree B. fraction showed it to contain 23.8% unsaturated hydrocarbons and 72.2% aromatic hydrocarbons. plete analysis of the heavier fractions by the method of procedure above outlined due to solidication on nitration. ADetermination of the con- .tent of aromatic hydrocarbons in` the heavier fractions was not possible by any known method of analysis. In order to determine the anti-detonating characteristics of the various components of the crude distillate product, runs were made in the test engine above describedusing blends of the various fractions with the straight run Pennsylvania gasoline as motor fuels. Separate runs were thus made'using blends composed of 20% of the first four fractions listed above with 80% of the straight run Pennsylvania gasoline and in each case it was found possible to operate .without audible detonation at a substantially higher compression ratio than that at which detonation became audiblewhen using a blend of 20% pure benzol and 80% of the straight run gasoline as the motor fuel. Another similar test was made with a blend composed of of the 10 degree B. gravity fraction with 85% of the straight run gasoline and in this case it also was found possible to operate without audible detonation at a compression ratio higher than that at which detonation became audible when using the /80% benzol blend. j

A number of these intermediate and heavier fractions were found to have properties which make them of especial value as paint thinners. For example, a number of fractions having gravities ranging from 13 to 34 degrees B. when used as paint thinners were found to give good distribution and although they had relatively high flash and boiling points, dried readily and without discoloration. The heavier distillates were also found to have an exceptionally low viscosity and exceptionally low cold test as compared to ordinary petroleum distillates of the same gravity. For example, the 22.6 degree B. fraction was found to have a net viscosity of 300 at 60 degrees F. as measured by a standard thermoviscosimeter, the 11.3 degree B. fraction to have a net viscosity of 650 at 80 degrees F. as indicated by the thermo-viscosimeteror 54 seconds Saybolt at 80 degrees F., while the heaviest of the above fractions, having a specific gravity of 1.058, was found to have a viscosity of 184'seconds Saybolt at 80 degrees F. and to solidify at minus degrees F.

The freezing points of the 39.7 degree B. fraction and of the 32.8 degree B. distillate, ob-

tained by redistillation of the crude distillateproducts from the' runs given as Examples 5 and 3 respectively as above described, were found to be below minus 40 degrees F., notwithstanding the large percentage of aromatic hydrocarbons contained in these distillates. The actual freezing point of these distillates was not determined because minus 40 degrees F. was the lowest temperature which could be obtained with the testing equipment used, although at this temperature both of these distillates were perfectly uid and would 4not solidify even onwthe addition of benzol seed crystals.

I claim:

1. `As a product of manufacture an overhead cracked petroleum distillateboiling substantially below 450 degrees F. and having approximately the boiling pointcurve of straight run petroleum gasoline and comprising in excess of 50% aro- It was impossible to obtain a comherein described.

`2. As a product of manufacture an overhead cracked petroleum distillate boiling substantially below 450 degrees F. and having approximately the boiling point curve of straight run petroleum gasoline and comprising in excess of 80% aromatic. hydrocarbons as determined by the method herein described.

3. As a motorfuel for internal combustion engines an overhead cracked petroleum distillate boiling substantially below 450 degrees F. and having approximately the boiling point curve of straight run petroleum gasoline comprising in excess of 50% aromatic hydrocarbons having a gravity between 28 and 34 degrees B. Y

4. As a product of manufacture a crude cracked petroleum distillate produced by a vapor phase crackingroperation conducted so as to avoid substantial carbon formation which on redistillation will give an overhead distillate boiling substantially below 450 degrees F. and having approximately the boiling point curve of straight run gasoline which will contain in excess of 50% aromatic hydrocarbons.

5. The improvement in the art of cracking petroleum oils comprising forcing the oil to be treated through an elongated heating zone in a stream of restricted cross section, heating the oil during its passage therethrough to. vaporizetheoil and crack it in the vapor phase by positively circulating a. heating medium in indirect heat exchanging relation therewith and controlling the temperature of the heating medium and the rate of flow of ,oil vapors to maintain the vapors at a temperature greater than 900 degrees F. and less than 1200 degrees F. for the time required for the vapors to travel through a 1' coil at least 350 feet long when4 supplied at. a rate corresponding to the vapor equivalent of 180 gallons per hour of liquid oil and to produce a crude product which when fractionated will give a distillate having approximately the boiling point curve of straight run gasoline and comprising in excess of 50% aromatic hydrocarbons.

heat to the vapors to maintain a high rate of v heat input with a low temperature differential between the oil vapors and the medium from which heat is transmitted thereto and the rate of flow of the vapors through said heating zone to avoid substantial carbon formation and to maintain the vapors at a temperature greater than 900 degrees F. and less than 1200 degrees F. for the time required ior the vapors to travel through a 1" coil at least 350 feet long when supplied at a rate corresponding to the vapor equivalent of 180 gallons per hourof liquid oil thereby producing a crude product which when fractionated will give a distillate having approximately the boiling point curve of straight run gasoline and containing in excess of 50% aromatic hydrocarbons.

7. The improvement in the art of cracking hydrocarbon oils comprising forcing 'the oil to be treated through an elongated heating zone in a stream of restricted cross section, heating the oil during its passage therethrough to a temperature in excess of 975 degrees F. by positively circulating superheated 'steam in indirect heat exchanging relation therewith and regulating the rate of flow of oil and the temperature of the superheated steam passing in heat exchanging relation therewith toconvert in excess of 20% of the oil charged into aromatic hydrocarbons without substantial coke formation and recycling uncondensed steam which has passed in heat exchanging relation with the il through a heater to the heating zone to pass again in indirect heat exchanging relation with the oil being treated.

CHAUNCEY B. FORWARD. 

